Portable electronic devices such as mobile phones, smart phones, personal digital assistants (PDAs), and tablets have become popular and ubiquitous. More and more features have been added to these devices, such as navigation applications for vehicles or individuals, which often rely on GNSS (Global Navigation Satellite Systems) signal reception and processing functionality. GNSS is a standard generic term for satellite navigation systems that provide geo-spatial positioning signals with global coverage, and which include a plurality of satellites which orbit the earth in extremely precise orbits and can transmit radio signals to any of a number of GNSS receiving modules. One well-known fully operational GNSS is the United States' Global Positioning System (GPS), formally known as NAVSTAR. An electronic device with a GPS module having an antenna and receiver allows a location (longitude, latitude, and altitude) to be determined using the signals transmitted from four or more GPS satellites, which signals also indicate an accurate corresponding time. Using geometric triangulation, the three known positions can be used to determine a two dimensional location (latitude and longitude). Obtaining a signal from a fourth satellite can allow a calculation of a three-dimensional location (latitude, longitude and altitude).
The satellite signals can be problematic in that a line-of-sight from a satellite to the receiver is required, and can be blocked by various obstructions such as tall buildings, certain land features, and within buildings.
Navigation applications can also take advantage of other systems for sensing location. For example, an inertial navigation system (INS) can include an inertial measurement unit (IMU), which uses a combination of accelerometers and gyroscopes to measure position, velocity, orientation (attitude), and gravitational forces on a vehicle or individual. In general, an IMU works by detecting acceleration using one or more accelerometers, and by detecting changes in rotational attributes like pitch, roll, and yaw using one or more gyroscopes. Relative position and orientation can then be computed using a method known as dead reckoning. Such a method can be problematic in that the data is relative and measurement errors are cumulative.
Electronic systems having both GPS functionality and INS functionality are known, and combining GPS data and INS data can provide a more accurate determination of location.